You have a very short window in which to socialize your yorkie so that you don't have a yapper. They say they should be socialized very well before they are sixteen weeks old. That means they should experience every sort of situation, such as, walks, taking them to work with you (if possible), take them to visit other people in their homes, especially those with other small doggies, play dates with other tiny doggies; take them shopping, and into lots of different types of buildings (where allowed). Take them to ball games. Allow them to become familiar with small children and teenagers. Give them every kind of experience you possibly can and you will more than likely have a very well-rounded and sociable yorkie. Mine doesn't yap and I did all of these things with her before the age of sixteen weeks. So, get your rest now, because you're going to need it!
I almost forgot to have people come and ring the doorbell so they won't become yappy over that, too.